Compliance with procedures for monitoring individuals at risk to toxic agents is facilitated when these procedures can be implemented easily and inexpensively. The system described here is designed to draw less than a microliter of blood with a single-use consumable and perform an assay on the sample in the consumable using a hand-held monitor. This instrument performs the analysis, calculates and displays the result, holds it in memory for recall, and interfaces with data collection systems. The consumable, which is the key component of the system, consists of a microcuvette and integrated needle, fabricated via silicon microlithographic technology. Development of the integrated needle (100 micrometer diameter) is the main objective of Phase I. Experimental consumables having needles with different dimensions will be fabricated and evaluated in puncture tests. A cholinesterase assay on whole blood will also be demonstrated in this device as a first step toward the development of a monitoring method for exposure to organophosphorus pesticides. This minimally invasive blood testing technology can be adapted to assay many other analytes for toxic monitoring and biodiagnostic applications. PROPOSED COMMERCIAL APPLICATION: The successful development of this microelectronic device has enormous potential to be used in field conditions to monitor the pesticide exposures. However, proper standardization of the device is required to differentiate the sensitivity of different pesticides within the same class and between classes of compounds.